PSI - Issue 2_B

Thomas Reichert et al. / Procedia Structural Integrity 2 (2016) 1652–1659 Thomas Reichert, Wolfgang Böhme and Johannes Tlatlik / Structural Integrity Procedia 00 (2016) 000–000

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Fig. 1. Fracture toughness K Jc,d and 5%-fractile lower bound curves according to ASTM E1921 of all test series of the previous project with varying specimen sizes and varying loading rates compared to the K IR -curve, SE(B) results from IWM and C(T) results from MPA.

2. Specimens and material

The fracture mechanics tests have been performed with reactor pressure vessel steel 22 NiMoCr 3 7, which had been used in other investigations on the applicability of the Master Curve concept at quasistatic loading rates Hohe et al. (2005) and Roos et al. (2006) and in the preceding project Böhme et al (2012). Results obtained were the characteristic Master Curve reference temperature for quasistatic loading T 0,stat. = -68 °C and a “Nil Ductility Transition Reference Temperature” of RT NDT = -20 °C. In the current project specimens have been extracted similar to Hohe et al. (2006) with cracks positioned between ⅔ and ¾ of the vessel’s thickness and with a crack orientation perpendicular to the vessel’s longitudinal axis, thus simulating a crack starting from inside the vessel towards the outer surface (T-S-orientation). All SE(B)-specimens were pre-cracked according to ASTM E1921 with a stress intensity factor K I of below 15 MPa √ m for the final 0.6 mm crack growth. The initial crack depth before testing was a/W = 0.3, which is the minimum ratio allowed by ISO/DIS 26843 in order to minimize impact induced vibrations and to obtain a linear increase in crack tip loading, see Böhme (1990). Specimens received 10% side grooves on each side, in order to achieve a relative straight crack front and a relative constant stress constraint along the crack front. 3. Experiments and measuring techniques Experiments with SE(B)40/20 specimens were performed at a 500kN rapid tensile testing machine with a three point bending test rig, see Fig. 2. For the evaluation of dynamic K Jc,d values according to ASTM E1921 and ASTM E1820 a load-crack mouth opening plot is required. Due to inertia effects, global force measurements at high loading velocities show oscillations, which cannot be used in an evaluation of the fracture toughness value. Therefore, a local type of force measurement was used with strain gauges applied close to the vicinity of the crack tip according to Böhme et al. (1983) and in the quarter point of the bending specimen according to ASTM E1820. Each measurement uses signals from two opposing strain gauges which have been averaged to mitigate any effect resulting from slightly asymmetric loading, see Fig. 2. In order to obtain a useable force signal at higher loading rates, a calibration of the strain gauge signals at a medium loading rate, at which inertia effects do not affect the measured global force, has been performed. The crack mouth opening displacement CMOD has been determined